A head-up display device is a transparent display which displays various pieces of information necessary for driving at the main viewpoint position of a pilot or a driver as a virtual image while overlapping the information with an external visual field, in order to minimize movement of the viewpoint of the pilot or the driver.
The head up display device, which includes a display unit, an optical system, a holographic combiner, etc., forms a designated image of driving information, such as current vehicle speed, position, etc., through the display unit, and projects the formed image onto the holographic combiner attached to a front window of the vehicle, i.e., a windshield, using the optical system. A designated image is formed in the air in the front region of the vehicle and the driver may view information regarding driving, such as the current position, speed, etc., through the formed image without requiring the driver to turn his/her head to loot at a dashboard of the vehicle.
Such a head up display system uses a cathode-ray tube (CRT) or a liquid crystal display (LCD) now, as a display unit to display information regarding driving of a vehicle as a designated image.
Light having image information having passed through an image panel is provided to a driver through a mirror or a windshield and, in this case, distribution of light incident upon the image panel may not be uniform and thus optical uniformity of the image provided to the driver may be lowered.
Particularly, a light emitting unit uses light emitting diodes, etc., but, in order to improve image quality in a head up display device, it is necessary to supply uniform light to the image panel while minimizing optical loss of light emitted from the light emitting diodes.